The present invention relates to adjusting mechanisms for use with a headlamp to adjust the position of a headlamp and retain the desired adjusted position.
A variety of headlamp adjusting mechanisms are currently available. These mechanisms typically provide a housing and a gearing arrangement retained in the housing for transferring rotary motion in one direction to a linear motion in another direction. The purpose for transferring rotary motion into linear motion is to control the movement and adjustment of the headlamp from a more conveniently accessible position. The remote control of the adjustment of the headlamp enables a variety of angular relationships to be achieved between a point where a user controls the adjustment of the headlamp and another point at which the adjustment actually occurs.
The angular relationships that can be achieved using a headlamp adjusting mechanism is very important to the automobile industry. In the automobile industry, space limitations for components in the operating compartment, or engine compartment, is very limited. As such, it is advantageous to provide a conveniently accessible adjusting point to adjust a remote and somewhat inaccessible headlamp adjusting mechanism.
A variety of headlamp adjusting mechanisms have been produced to provide remote adjustment of a headlamp. The following list provides an example of some known devices:
______________________________________ Inventor U.S. Pat. No. Issued ______________________________________ Lisak 5,079,676 01/07/92 Weber 5,034,870 07/23/91 Eckenrode 5,023,759 06/11/91 Ryder et al. 4,939,945 07/10/91 Lisak 4,893,219 01/09/90 Ryder et al. 4,757,429 07/12/88 Ryder et al. 4,674,018 06/16/87 ______________________________________
The devices as shown in Eckenrode and Weber directly transfer forces from a driving assembly to move a shaft axially through the housing. The other references presented hereinabove rotate and axially displace a shaft.
Each of the devices presented hereinabove includes an arrangement whereby a threaded shaft engages a cooperatively formed threaded bore to axially displace the threaded shaft through the housing. Each of the devices uses a specialized bushing or gear member having a tapped bore to provide cooperative threads for engaging the threaded shaft. A problem arises with these devices such that the specialized bushing or gear are not readily available and must be produced or molded especially for this application. As such, the cost of such bushings or gears can be quite expensive. Additionally, since these specialized bushings and gear members are specifically produced for this application, they may not be readily available and may create production problems if they become unavailable.
Prior art headlamp adjusting devices also attempt to provide additional friction or prevailing torque to retain a desired adjustment during use. In this regard, road and engine vibration will tend to move the components out of adjustment if the threaded engagement is free running. To this end, many devices provide such friction or prevailing torque but require numerous additional parts and locking devices to achieve the desired friction requirements. For example, several devices employ plastic bushings and thread portions of the housing to increase effective thread length through which the threaded shaft travels to increase the frictional engagement between the shaft and the threads. While this increased thread length may provide a degree of increased friction to retain the desired adjustment, the threads experience a degree of axial play and possibly deflection. Therefore, while the shaft may be prevented from the rotary movement, the shaft still moves forward and backward along the axis extending through the shaft. Such axial play is undesired as it potentially results in undesired adjustment of the headlamp attached to the headlamp adjusting mechanism.
Another problem encountered with the prior art headlamp adjusting mechanisms is axial deflection. As shown in the device in Eckenrode and Weber, the shaft is only retained over a short section in the threaded bushing retained in the housing. As such, there is a degree of axial deflection which may occur with this device. A variety of prior art devices which employ bushings may somewhat reduce the axial deflection, however, there is still some potential for the bushing in which the shaft is retained to axially deflect within the bore tapped in the housing.
As mentioned above, some prior art devices employ threaded sections of the housing to provide threaded engagement between the shaft and the housing. A commonly used material for the housing is plastic so that the weight, cost and time for production is minimized. While most plastic bushings rely upon a self tapping arrangement, viz., the metal thread cold forms the plastic material, if a thread is formed through a section of the housing, an error in tapping the thread through the housing makes the housing unusable for an adjusting mechanism. As such, the potential for scrap housings may be quite high. Additionally, the threads generally have a greater potential for stripping in the plastic material than if the housings were formed from a metallic material. While devices which use a tapped gear often times provide a metallic gear and therefore a metallic threaded surface, such gears can be quite expensive to produce and may create a supply problem as mentioned hereinabove.
Prior art devices also have a problem in that the degree of prevailing torque or friction employed to prevent movement of the shaft is not readily controllable. The components which control the prevailing torque, the specialized threaded bushings and specialized threaded gears, do not lend themselves to varying degrees of prevailing torque. For example, one way to change the degree of prevailing torque between the threaded shaft and the specialized bushings and gears would be to provide some kind of friction device on the gears to provide resistance against adjustment, as disclosed in U.S. patent application No. 07/800,536, filed Nov. 27, 1991, now U.S. Pat. No. 5,161,877. As mentioned above, however, this solution does not resolve the problem of axial play in the threaded shaft.
Another way to control the degree of prevailing torque imposed on the threaded shaft might be to alter the tolerances between the threaded shaft and the specialized threaded bushings or gears. This solution, however, results in further specialization of the bushings, threaded gears, and threaded shaft and therefore does not solve the problems of costs and availability.
One further prior art device provides a threaded shaft which has a partially spherical end for engaging a cooperatively formed socket attached to a headlamp. The shaft is axially displaced by means of a gearing arrangement in the housing of the adjusting mechanism. The shaft is prevented from rotating by a number of wings or ears protruding from the partially spherical end of the shaft. The wings or ears engage cooperatively formed slots in the socket. This device provides a degree of multi-directional movement between a partially spherical and the shaft and the socket. It is believed that this is provided to increase the prevailing torque or resistance to adjustment of the shaft in the adjusting mechanism housing. This device has a potential problem, however, such that the wings or ears are prone to being broken off if not properly installed in the socket.